CO<sub>2</sub> Capture and Electrochemical Reduction of Low-Concentration CO<sub>2</sub> Using a Re(I)-Complex Catalyst in Ethanol
Masahiko Miyaji, Yusuke Tamaki, Kei Kamogawa, Yuto Abiru, Manabu Abe, Osamu Ishitani
Abstract
Direct reduction of low-concentration CO 2 from exhaust gases (3–13%) is important for CO 2 utilization technologies because CO 2 condensation processes require high energy consumption and cost. The Re(I) ethoxide complex fac -[Re(bpy-CH 2 OH)(CO) 3 (OEt)] (bpy-CH 2 OH = 4,4′-bis(hydroxymethyl)-2,2′-bipyridine), which is formed in an EtOH solution containing a base, efficiently captured CO 2 to form the carbonate-ester complex fac -[Re(bpy-CH 2 OH)(CO) 3 (OCOOEt)] ( Re(OCOOEt) ) under both 10% and 100% CO 2 atmospheres. In an EtOH solution containing 1,1,3,3-tetramethylguanidine (TMG) as the base, the electrocatalytic CO 2 reduction reaction proceeded by Re(OCOOEt) with high CO selectivity, Faradaic efficiency, and durability even under a 10% CO 2 atmosphere. This high electrocatalysis was retained in the presence of water in the solution up to 2.8 M (5 vol %). On the other hand, the electrocatalytic CO 2 reduction reaction did not proceed efficiently in the absence of TMG under 10% CO 2 . The mechanistic studies and investigation suggest that the formation of the carbonate-ester complex in advance is necessary for the highly efficient electrocatalytic reduction of low-concentration CO 2 in EtOH.